Hydraulic tap changer

ABSTRACT

A step-switching arrangement for changing the taps on a transformer winding without interrupting the flow of current from the winding to a load line includes a precontact switch and a current-limiting resistance connected in a series circuit extending from the transformer tap changing contacts to the load line, this circuit being paralleled by a circuit containing a changeover switch and vacuum switch connected in series and also extending from the tap-changing contacts to the load line. A circulating current through the switches and resistance and part of the transformer winding occurs during a change in taps, and this circulating current is interrupted by opening the contacts of the vacuum switch. All of the switches are actuated by hydraulic motors of the linear type, the motors being supplied from hydraulic pumps of the linear type which are operated in synchronism with the tap-changing mechanism so as to obtain the necessary operating sequence for the various switches in changing over from one tap to another.

United StatesPatent 3,359,485 12/] 967 Buehler Heinz 'lrachsel Inventor Nussbaumen, Switzerland Appl. No. 22,532 Filed Mar. 25, 1970 Patented July 20, 1971 Assignee Aktiengesellschaft Brown Boveri & Cie

Baden, Switzerland Priority Apr. 2, 1969 Switzerland HYDRAULIC TAP CHANGER 5 Claims, 1 Drawing Fig.

U.S. CI 323/435 R, 200/ l 8 Int. Cl "01f 29/04 Field of Search 200/82 A, 82 8,144 B, 144 AP, 146 AA, 18; 323/435 R References Cited UNITED STATES PATENTS FOREIGN PATENTS Primary Examiner-J. D. Miller Assistant Examiner-A. D. Pellinen AttorneyPierce, Scheffler & Parker ABSTRACT: A step-switching arrangement for changing the taps on a transfonner winding without interrupting the flow of current from the winding to-a load line includes a precontact switch and a current limiting resistance connected in a series circuit extending from the transformer tap changing contacts to the load line, this circuit being paralleled by a circuit containing a changeover switch and vacuum switch connected in series and also extending from the tap-changing contacts to the load line. A circulating current through the switches and resistance and part of the transformer winding occurs during a change in taps, and this circulating current is interrupted by opening the contacts of the vacuum switch. All of the switches are actuated by hydraulic motors of the linear type, the motors being supplied from hydraulic pumps of the linear type which are operated in synchronism with the tap-changing mechanism so as to obtain the necessary operating sequence for the various switches in changing over from one tap to 323/435 another.

36 [34 39 42 58 37 59 45 O 38 30 55 O E O 57 49 I f :17 50 52 7 28 32 jug 57 i1 13a 54 13 ti conjunction with a first, or

nected via .a switchover currentJimiting resistance in series 1'"! pp tus, thc

oti'anycontact burnoff. j

-, avnssuuc .rsr cannons therewith to the transformer load line, the series circuit connection of the precontact switch and current-limiting resistance being paralleled by. another circuit containing a vacuum. switchjin series with a changeover switch.

A control device. for step transformers is known wherein the tap can be preselected, without current, by a step selector and the uninterrupted load switching occurs by way of a switchover. resistance and a vacuum switch arranged in parallel circuits to load line, there being a mechanically actuated switch assigned to. each; circuit, and the control of the mechanical switches and-vacuumswitch being effected by a v 7 With reference now to the common drive by way of a suitable all mechanical transmisv sion. However, because of the required sequential operations of the various switches, such-mechanical transmissions'arc I necessarily complicated intheir design and are subject to considerable wear. in switching back and forth, a he transformer tapsare changed, the two mechanically. actuated switches Y j must beope atedin such sequence that the one included in the circuit in series with the switchover resistance must always be operated first'as a so-called-precontact while the other mechanical switch. includedin the circuit .in series with the vacuum switch" switches without current.

. The object of thisinvention is to provide a moresimple and safe solution for deriving correct sequential operation'of ali three of the switches involved, that is, the precontact switch, the changeover switch and the vacuum switch by "utilizing a drive which executesan oscillatory movement in the changeoverof onetap to another on the transformer winding, this drive ttot'lpied to and; actuating pistonslof hydraulic, pumps ofth'elinenr type which are connectedwith douhlc-actingfhydraulic motors of the'linear type whose pistons are connected respectively to, the contacting actuating members of the three switches.

More particuiarlygthe inventionv provides, for effecting a reciprocating movement of the working pistons coupled to the precontact and changeover switches, a symmetrically arranged pump p'air'coupled to the-oscillatory drive, each directionof. mov ment of the. drive having assigned to it a pump which is effective for thatdrive direction but ineffective in; thcfothcr direction of movement of the drive. The piston of the pump for effecting operation of the piston of the hydraulic motor which actuates the contacts of the vacuum switch is effectivein each'dircction of movementof the oscillatory drive to execute a double: stroke; and the piston of the hydraulic motor assigned. to. the. vacuumswitch controls, by'a hydraulic connection, the piston of s control valve interposed in the hydraulic connectionsbctweenthe pump cylinders assigned to the'hydraulic motors which actuate respectively the contacts of the precontact and changeover. switches in order to effect the. necessary control of: motors in relation 'to opening 'f andclosing operations ofthscontacts of the vacuum switch.

In. addition to a high degree of freedom in the-spatial arrangement of the individual hydrauliccomponents of the tapchangvacuumswitch has the further advantage,

due to the constant delivered that the opening stroke: is constant and independent The fote'g0ing as well asotheradvantagesinherent in the improved in accordance with the invendors will; more apparent from the following detaileddcscr'iption-of one suitable. embodiment thereof and from thesocompanying drswing the single view. of which is a combined electrical and hydraulic schematic.

quantity. of hydraulic fluid, e.g., oil,

. cylinder which acts on drawing, the tapped transformer winding is indicated at l, and taps alongthe winding are indicated at a and 1:. Obviously more than this number of taps are provided along the winding but the two which have been illustrated are sufficient to explain the inventive concept. Tap a and others similar to it are associated with one tap selector movable contact 2, and tap b and others similar to it are associated with a second tap selector movable contact 3. The movable contact members 2 and 3 are associated with and move alongin contact with conductor rails 2a and 3a, respectively. I

Conductor rail 2a is connected to contact 4 of a so-called precontact switch 6, and conductor rail 3a is connected to contact Sof this switch. The switch arm 6a pivotally mounted at 16 is movable back and forth between contacts 4 and 5 and is actuated by a piston 17 movable back and forth within cylinder 18, the latter including a slot l9 to receive the switch arm 6a. The switch arm 6a is also electrically connected through a current-limiting resistant 7 to the load line U.

Conductor rail 2a is also connected to one'main switching contact 8. of a changeover switch 12, and conductor rail 30 is connected to another main switching contact 11 of switch 12. The switching arm 12a pivotally mounted at 20 is movable back-and-forth between contacts 8 and 11 and is actuated by a piston 21 movable back-and-forth within cylinder 22, the latter including a slot 23 to receive switch arm 12a. The switching arm [20 is also electrically connected throughthe contacts of a vacuum switch 13 to the load line U. The movable contact 130 of the vacuum switch is-actuated between open and closed'position by means of a piston 23 operating within cylinder 30, there being a return spring 29 within the piston 28 in the contact closing direction.- 7 r r in addition to themain switching contacts B and ll, the changeover switch 12 includes two auxiliary contacts 9 and 10 located'in the path of switch arm between the endmost contacts 8 and 11. Connected in an auxiliary circuit with auxiliary contact! isa fuse 14 which connects with the circuit leading to conductor rail 20 and, in a similar manner, a fuse 15 is connected in an auxiliary circuit leading from auxiliary con tact 10 to conductor rail 34'.

The step. selector mechanism which moves the'contact members] and 3.along the taps of the transformer winding is of conventional construction and hence has not been detailed as to-its specific mechanism. f

in order to explain" the mode of operation of the" step switching arrangement, the electrical schematic shows, for example, that tap selector contact 2'is' on tap a. and tap selector contact 3 is-on 'tap 'b. Switch 6 is in the position indicated on the drawing wherein switchv arm 6a in the solid line position is engaged with contact 4. Switch 12 is in the position indicated wherein the switch arm 12a in the solid line position is engaged with tbemain switching contact 8.

The contacts of the vacuum switch are closed and hence an electrical circuit is completed from transformer winding tap 2 to the load line U' which can be traced from conductor rail 2a through switch contact- 8, switch am 1 20 and-the vacuum switch 13. Another circuit to the load line U is completed from conductor rail'22 through switch contact 4, switch arm 6aand resistance 7 but this circuit willcarry very little current due tothepresence of resistance'7 and the factthat the circuit through switches]! and practically short circuits the circuitpath through switehti.

inorder to changeover fromtape'to-the next tap'b, switch 6 is actuated to shift contact arm 64 fromcontact 4 to contact 5. This completes temporarilya circuit. from conductor rail 3a through switch 6,. resistanceTvacuum switch Band switch I 2 to conductor rail 24 thuscausing'a circulating current, limited by resistance 7 to flow in that part of the transformer winding latory current through part of thetransformer" winding, and

b also commutating the flow of load current to line U from contact member 2 to contact member 30f the tap selector.

Vacuum switch 13 then recloses its contacts and the chan- 1 geover switch l2 is actuated so that contact arm 12a now engages the main switching contact 11, and a direct path from tap b'to the line U is completed through the series connection of the two switches 12 and 13. This'completes the changeover from tap a to tap b.

The thre'episton cylinder units associated respectively with v the switches 6, '12 and 13 are controlled in the following mannerin order to effect their required sequential operation for changing from one tap to another on, the transformer winding. 7

An oscillatory drive plate 33 which is mounted for oscillation about an axis 35 is designed as an impulse drive, in known manner, and is coupled up to the tap selector mechanism, not shown, by which the movable contacts 2 and 3 are shifted in alternation along'the taps of the transformer winding, such that drive plate 33 rotates in a clockwise direction for a change from a first to asecond tap on the winding, and then in a counterclockwise direction for a change from the second to a third tap on the winding, then back in a clockwise direction,

etc. thus oscillating back-and-forth for successive tap changes along the winding as indicated by arrows 34. The oscillatory lationof drive plate 33 such that as the plate executes a counterclockwise movement, piston 42 will be forced into one end of cylinder45 and'piston 40 will be withdrawn from the op posite end of cylinder 43. Conversely, when drive plate 33executes clockwise movement, piston 40 will be forced into one 'endof cylind'er43 and'piston 42 willbe withdrawn from the 'opposite'end of cylinder "45. Piston 41, on the other hand, is located in the position shown in the drawing when crankpin 36 is in the limit position depicted and is also located in the same position when plate 33 has rotated counterclockwise to its other limit position. Piston 41 this obviously moves into its cylinder 44the same predetermined distance and is returned to its starting position eachtime plate'33 moves clockwise, or counterclockwisefrom one of its limit positions to the other,

i "the piston reaching its deepest point in the cylinder at one-half the angle of oscillation of-plate 33. Pump cylinder 44 is connected via an oil line 31 with the hydraulic motor cylinder 30 'at the side of piston'28 opposite the biasing spring 29.

Pump cylinder 43 is permanently connected with the surrounding oil space containing the various elements of the p load-switching device via port 46, and pump cylinder 45 is I similarly connected with that oil space via port 47. Pump cylinder 4'4 is provided witha port 48 which is passed over and I I c'losed by piston 41 during each inward movement thereof. Ports 49, 50 of pump cylinders 43, 4 communicate in a direct manner via oil lines 27, 26 with the opposite ends of the hydraulic motor cylinder 18. Similarly, ports 51, 52 of pump cylinders '43, 45 communicate via oil lines 53, 54 with the opposite ends of the fhydrat ilic motor cylinder 22 but in an indirectmanner through the intermediary of a control valve ineluding a valve amnsa operating in a reciprocating manner within a valve cylinder 55 and oil lines 24, 25. Valve piston 56 is biased to its upper end position depicted in the drawing by a located in the lower end of the cylinder 55 and lower end of piston 56. The upper end ofvalve cylinder55 is connected via oil line 32 with motor cylinder 30 at'the side ofpiston 28 in which the biasing spring 29 is located. x

The pump cylinders 43', 45 are also provided with overflow I channels 58, 60'and 59, 61 respectively. The cylinders 18 and ticulated to piston 41 which works in cylinder 44 of still 1 another linear-type hydraulic pump. The two pump units 43 and 42-45 are symmetrically arranged in relation to oscil- 22 of the hydraulic motors are mounted on and electrically insulated from a suitable support, and at least the end portions of the oil lines 24, 25 and 26, 27 terminating at these cylinders are electrically insulated therefrom since during the switching operations, switchcs6 and 12 mounted on these cylinders carry different electrical potentials. Cylinder 30 is also mounted on and electrically insulated from a suitable support and atleast the end portions of the oil lines 31, 32 are electrically insulated therefrom since piston 28 is connected tothe movable contact 13a of the vacuumswitch 13 which also carriesapotential. I

The required sequential operation of the hydraulic pumps and motors in changing from one tap to another on thetransformer winding is as follows:

In the position depicted on the drawing, the movable contact member 2 of the tap selector mechanism is on contact a, as previously explained and current flow is from this tap through rail 20, switch 12 and switch, 13 in series to the load line U. The switchover to the next tap b is prepared by the movable tap selector contact 3. Drive 33 is now actuated in a counterclockwise direction indicated by the lower arrow 34. As soon as piston 42 moves inward of cylinder to the point where itcloses port 47, a delivery of oil takes place from this cylinder through line 26 to the right end of the hydraulic motor cylinder 18 thus shifting piston 17 to the left from the position indicated on the drawingso that switch arm 6ais rotated counterclockwise thus transferring the arm from contact 4 to contact 5. The switch arm 6a, and also switch arm 12a of switch 12 are each preferably provided withan overcenter mechanism, not illustrated, which acts in both directions of movement of the switch arms so that when the piston 17 (or piston 21) has been shifted in its cylinder for a distance corresponding to pivotal movement of the switch arm 6a (or 120) a little more than one-half the full angle of movement of the switch arm, the overcenter mechanism takes over and quickly shifts the switch arm to its opposite end position owing towhich switching at switches 6 and 12 takes place independently of any contact bumoff.

Assoon as switch arm 60 arrives at contact 5, a flow of circulation current limited by resistance 7 is initiated in the manner previouslyexplained. Meanwhile, piston 41 has now passed over and closed port 48 in cylinder 44 so that oil is now pumped from this cylinder via line 31 into cylinder 30 under the piston 28 thus actuating the movable contact member 13a of vacuum switch upward to break the contacts of this switch and thus interrupting the circulation current, and causing the load currentflowing to line U to be commutated to the selector contact 3 via switch contact 5 and resistance 7.

As piston 28 rises in its cylinder, oil is forced via line 32 into the upper end of valve cylinder 55 to force valve piston 56 downward owing to which, at a time when vacuum switch 13 has already interrupted the circulation current, oil flows into line 25 now cleared by the valve piston 56, from pump cylinder 45 viaport 52 and line 54, with ports 50 and 59 closed meanwhile, and thence into the right end of motor cylinder 22 causing displacement of piston 21 from right-toleftand actuation of switch arm 12a from contact 8 to contact 11 via contacts 9 and 10. Due to the return movement of piston 41 to the position depicted in the drawing, the contacts of vacuum switch 13 reclose under the action of the biasing spring 29 and take over the load current, thus completing a drawing, the two. hydraulic pumps. 42-45 and 40-43 exchange their roles in which, pump 4043 becomes the operative pump to effect a shifting of the motor piston 17 from left-to-right in its cylinder 18 and actuation of switch arm 60 from contact 5 to contact 4.

the contacts of the vacuum switch 13 fail to open and interrupt the circulation current, switch arm 12a shifts from contact 8 to contact 9. The are voltage of the switching arc is then high enough for the current to reliably commutate from contact 8 to contact 9, and the circulation current is then interrupted by blowing of fuse l4 and the load current is shifted to the circuit branch containing the switchover resistance 7. Contact arm 12a then switches without current via contact to contact 11. When fuse l4 responds (blows) the step switch drive is stopped and thus prevents any damage from being done to the step switch or to the transformer.

While, for the purpose of illustrated the invention, a singlephase example'of construction has been illustrated, it is selfevident that the improved tap changing device can be readily applied to a three-phase embodiment, the drive 33 then being advantageously provided with three of the crankpins 36 arranged l20 apart, and the hydraulic pumps being disposed for example, in a star arrangement.

lclaim:

l. in a stepswitching device for changing the taps on a transformer winding connected to a load line, the combination comprising a tap selector mechanism including at least two contact members movable sequentially along different taps of the transformer winding, a precontact switch including two stationary contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectively connectable with said stationary contacts, a first double-acting hydraulic motor the piston of whichis connected to said movable contact member of said precontact switch, a resistance element connected between said movable contact member of said precontact switch and said load line, a changeover switch including two stationary contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectably connectable with said stationary contacts, a second double-acting hydraulic motor the piston of which is connected to said movable contact member of said changeover switch, a vacuum switch connected between said movable contact member of said changeover switch and said load line, a third hydraulic motor the piston of which is connected to and controls the opening and closing of the contacts I of said vacuum switch, a drive mechanism actuated in synchronism with said movable contact members of said tap selector mechanism, first and second single-acting hydraulic pumps the pistons of which are connected to said drive mechanism such that said hydraulic pumps execute pumping strokes in alternation as said drive mechanism executes consecutive movements correlated to consecutive movements of said contact members of said tap selector mechanism, a first set of outlet ports from said hydraulic pumps connected via hydraulic lines directly to opposite ends of the cylinder of said first double-acting hydraulic motor, a second set of outlet ports from said hydraulic pumps connected via hydraulic lines indirectly to opposite ends of the cylinder of said second double-acting hydraulic motor through a control valve, a third sin gle-acting hydraulic pump connected to said drive mechanism such that said pump executes one pumping stroke for each movement of said drive mechanism, a hydraulic line extending from an outlet port from said third hydraulic pump to the cylinder of said third hydraulic motor at one side of the piston for twice actuating the piston and the vacuum switch contacts to open and closed position for each movement of said drive mechanism, and a hydraulic line extending from the cylinder of said third hydraulic motor at the other side of the piston therein to the cylinder of said control valve for actuating the piston therein to control flow of hydraulic fluid in the lines extending to the cylinder of said second double-acting hydraulic A step-switching device as defined in claim 1 for changing the taps on a transformer winding wherein said drive mechanism is arranged to effect an oscillatory movement, and wherein the pistons of said hydraulic pumps are connected with said drive mechanism by means of connecting rods articulated to a common crankpin.

3. A step-switching device as defined in claim 2 for changing the taps on a transformer winding wherein the connecting rod and piston of said third hydraulic pump reach dead center position at the midposition of said oscillatory drive mechanism.

4. A stepswitching device as defined in claim 1 for changing the taps on a transformer winding and wherein said third hydraulic motor includes a biasing spring loading the piston therein to a position wherein the contacts of said vacuum switch are closed, and the admission of hydraulic fluid from said third hydraulic pump acts against the piston to open the vacuum switch contacts in opposition to said biasing spring.

5. A step-switching device as defined in claim 1 for changing the taps on a transformer winding wherein said control valve includes a biasing spring loading the piston therein to a position wherein fluid flow through the valve is cut off and the admission of hydraulic fluid into the valve cylinder from the cylinder of said third motor acts against the piston to open the valve in opposition to the biasing spring. 

1. In a step-switching device for changing the taps on a transformer winding connected to a load line, the combination comprising a tap selector mechanism including at least two contact members movable sequentially along different taps of the transformer winding, a precontact switch including two stationary contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectively connectable with said stationary contacts, a first double-acting hydraulic motor the piston of which is connected to said movable contact member of said precontact switch, a resistance element connected between said movable contact member of said precontact switch and said load line, a changeover switch including two stationary contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectably connectable with said stationary contacts, a second double-acting hydraulic motor the piston of which is connected to said movable contact member of said changeover switch, a vacuum switch connected between said movable contact member of said changeover switch and said load line, a third hydraulic motor the piston of which is connected to and controls the opening and closing of the contacts of said vacuum switch, a drive mechanism actuated in synchronism with said movable contact members of said tap selector mechanism, first and second single-acting hydraulic pumps the pistons of which are connected to said drive mechanism such that said hydraulic pumps execute pumping strokes in alternation as said drive mechanism executes consecutive movements correlated to consecutive movements of said contact members of said tap selector mechanism, a first set of outlet ports from said hydraulic pumps connected via hydraulic lines directly to opposite ends of the cylinder of said first double-acting hydraulic motor, a second set of outlet ports from said hydraulic pumps connected via hydraulic lines indirectly to opposite ends of the cylinder of said second double-acting hydraulic motor through a control valve, a third single-acting hydraulic pump connected to said drive mechanism such that said pump executes one pumping stroke for each movement of said drive mechanism, a hydraulic line extending from an outlet port from said third hydraulic pump to the cylinder of said third hydraulic motor at one side of the piston for twice actuating the piston and the vacuum switch contacts to open and closed position for each movement of said drive mechanism, and a hydraulic line extending from the cylinder of said third hydraulic motor at the other side of the piston therein to the cylinder of said control valve for actuating the piston therein to control flow of hydraulic fluid in the lines extending to the cylinder of said second doubleacting hydraulic motor.
 2. A step-switching device as defined in claim 1 for changing the taps on a transformer winding wherein said drive mechanism is arranged to effect an oscillatory movement, and wherein the pistons of said hydraulic pumps are connected with said drive mechanism by means of connecting rods articulated to a common crankpin.
 3. A step-switching device as defined in claim 2 for changing the taps on a transformer winding wherein the connecting rod and piston of said third hydraulic pump reach dead center position at the midposition of said oscillatory drive mechanism.
 4. A step-switching device as defined in claim 1 for changing the taps on a transformer winding and wherein said third hydraulic motor includes a biasing spring loading the piston therein to a position wherein the contacts of said vacuum switch are closed, and the admission of hydraulic fluid from said third hydraulic pump acts against the piston to open the vacuum switch contacts in opposition to said biasing spring.
 5. A step-switching device as defined in claim 1 for changing the taps on a transformer winding wherein said control valvE includes a biasing spring loading the piston therein to a position wherein fluid flow through the valve is cut off and the admission of hydraulic fluid into the valve cylinder from the cylinder of said third motor acts against the piston to open the valve in opposition to the biasing spring. 